听力原文：A disturbing report appeared recently in the magazine Science. The report describ

听力原文： A disturbing report appeared recently in the magazine Science. The report describes an experiment, the results of which suggest that there are occasions when psychiatrists, doctors trained in the treatment of mental illnesses, have great difficulty in distinguishing between people who are mentally ill and those who are mentally healthy.

In the experiment, eight perfectly normal people pretended to have mental disorders and received psychiatric treatment in a number of different hospitals. The eight false patients included several trained doctors, who lied about their occupation. They also lied about their names and naturally about their symptoms. But in all other respects they told the truth concerning their lives and their personal relationships; and once they had been admitted to hospital they behaved quite normally.

However, as soon as they had been officially labeled "mentally ill", everything they did tended to con firm the diagnosis in the eyes of the medical staff. For if instance, if one of the "patients" approached a doctor and asked a perfectly sensible question such as "Pardon me doctor, could you tell me when I will be allowed to use the tennis courts？" The doctor's normal response was "to walk straight on, ignoring the question".

The eight false patients stayed in the mental institutions for periods of from 7 to 52 days. They are forced to the frightening conclusion that once a person has disappeared behind the walls of a mental institution, it may prove extremely difficult to convince the medical authorities that he or she is not in fact mentally ill.

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A．They were the subjects in a medical experiment.

B．They wanted to distinguish between people who are mentally iii and healthy.

C．They wanted to find out what happened to patients at mental institutions.

D．They were psychiatrists who experimented With new methods of treatment.